Conventional night vision devices are purged and nitrogen filled to protect optics and electronics over a range of temperatures. Temperature extremes cause condensation to occur within the devices which, in turn, cause the night vision devices to degrade or fail. There typically is no indication to the user of loss of nitrogen within the device, other than a system failure. These devices are, therefore, serviced on a regular basis in order to remove moisture from the device and purge the system with nitrogen.
There are systems, however, that include desiccants within their housing to help capture moisture from the environment. Desiccants are used in many electronics and food storage applications to help reduce and control moisture, or humidity within the housing. These desiccants provide a longer lifetime for the system, but once saturated with moisture, the system may still degrade or fail.
Indicating desiccants are used in some devices in order to alert the user of the device that the desiccant is saturated and no longer effective in removing moisture from the housing. These indicating desiccants typically change color to alert the user that the desiccant is no longer effective. The system is then typically serviced to remove the desiccant and a fresh desiccant is inserted in the housing.